Grain drier and method of drying grain

ABSTRACT

A grain drier system is disclosed which includes means for collecting heated air which has passed through grain and conducting it to the inlet of the burners which supply the heated gas to dry the grain. The collected air is introduced into the inlet of the burner at the periphery of the air stream to the burner in an area where the contact between the collected air and the flame of the burner is minimized. This procedure enables the heat of the collected air to be utilized without the likelihood of subjecting any entrained material to the action of the flame of the burner. 
     In order to further minimize the possibility of fire, prior to being conducted to the burner, the collected air is passed into a plenum where the velocity of the stream of collected air is decreased and its direction of movement changed so that a substantial portion of entrained dust and organic material is caused to fall out of the air stream. 
     Cleanout doors and dump doors for rapid cleaning and unloading of, respectively, the drier are also disclosed.

This is a division of application Ser. No. 06/306,66, filed on Sept. 29,1981, now U.S. Pat. No. 4,411,620.

The present invention relates generally to a grain drying and moreparticularly to a grain drier and method which can reuse heated airwhich has been passed through grain and can efficiently utilize theresidual heat in the grain after drying and which includes variousfeatures which cooperate to minimize the damage of fire.

In order to store grain efficiently, it is necessary to dry it to acondition in which it is less subject to molding or other deterioration.This is done by confining the grain between a pair of foraminous memberssuch as screens, perforated plates or the like and passing heated airthrough the grain which is thus confined. Since it is usually notdesirable to store the grain in the heated condition, it is necessary tocool the grain and this is accomplished by passing cool air through thegrain mass after it is dried. The cooling process results in a loss ofthe heat which is in the grain after drying. Because of the high cost ofenergy, a means to utilize the retained heat would materially decreasethe cost of drying.

Heretofore, attempts have been made to utilize the heat in the coolingair after it has passed through the hot grain by reintroducing it intothe section of the drive in which the drying occurs. These attempts havebeen generally unsatisfactory since the air which has passed through thegrain mass carries with it dust and organic matter which, when subjectedto the heat of the burner which elevates the temperature of the dryingair, often results in combustion of the dust and organic materials thuscausing fires inside of the drier. Once a fire has been started in agrain mass it is difficult to extinguish and the resulting damage isburned, scorched or smoke damaged grain and the damage to the equipmentis substantial.

Accordingly, it is the principal object of this invention to provide agrain drier and method which makes possible the reuse of air after ithas passed through the grain mass while minimizing the chance ofcombustion. It is a further object of the invention to provide a graindrier, which in the event of fire, may be rapidly unloaded so as tominimize the loss of grain and damage to the drier equipment. It isanother object of the invention to provide rapid means of removing dustand organic material from the drier during operation so that thebuild-up of dust and organic material in the drier can be minimized.

Other objects and advantages of the invention will become known from thefollowing description and the accompanying drawings in which:

FIG. 1 is an elevational view, partly in section of a drier embodyingvarious of the features of the invention;

FIG. 2 is a sectional view taken on line 2--2 in FIG. 1;

FIG. 3 is an exploded view illustrating the burner and duct constructionwhich constitutes a part of the device shown in FIG. 1;

FIG. 4 is a perspective view of the quick opening dumping device whichconstitutes a part of the grain drier shown in the preceding Figures;

FIG. 4A is a sectional view taken on line 4A--4A in FIG. 4;

FIG. 5 is a perspective view of the clean-out door construction whichforms a part of the drier shown in FIGS. 1-3;

FIG. 6 is an elevational view illustrating the one end of a portablegrain drier embodying various features of the invention;

FIG. 7 is a sectional view taken on line 7--7 in FIG. 6; and,

FIG. 8 is a section view of the grain drier of FIGS. 6 and 7 which ismodified to discharge heated grain.

In general, the method of the invention involves collecting the exhaustair or a substantial part thereof from the cooling section of the drierand conducting it to the inlet of the burners which supply the heatedgas to dry the grain. The exhaust air is introduced into the inlet ofthe burner at the periphery of the air stream to the burner in an areawhere the contact between the exhaust air and the flame of the burner isminimized. This procedure enables the heat of the exhaust air to beutilized without the likelihood of subjecting any entrained material tothe action of the flame of the burner.

In order to further minimize the possibility of fire, prior to beingconducted to the burner, the exhaust air is passed into a plenum wherethe velocity of the stream of exhaust air is decreased and its directionof movement changed so that a substantial portion of entrained dust andorganic material is caused to fall out of the air stream. Thisprocedure, in combination with the peripheral introduction of air, ishighly effective to minimize combustion of dust and organic material andthus results in a substantial supression of fires.

Now referring to the drawings, FIGS. 1 and 2 illustrate a grain drier 10embodying various of the features of the invention. The grain drier 10is of generally box-like construction and includes side walls 12 and 14and end walls 16 and 18. Inside the walls 12-18 a structure 20 isprovided for confining the grain so that it can be subjected to air flowto effect drying and cooling. The structure 20, illustrated, includesthree vertically aligned modules 22a, 22b and 22c.

The module 22a, which is the uppermost module, is positioned under agrain distributing trough 24 which extends the length of the drier 10and into which the grain 26 is distributed. The module 22a includes aninner wall structure 28 comprising a downwardly and outwardly slopingtop member fabricated from foraminous members 30 and 31, verticallyextending foraminous side members 32 and 33 and a foraminous bottommember 34. The inner wall structure 28 is adapted to receive heated gas(air and products of combustion) under pressure which passes outwardlythrough the foraminous members 30-33.

The grain 26 is conducted around the inner wall structure 28 byproviding an outer wall structure 35. The outer wall structure 35includes a pair of downwardly and outwardly sloping foraminous members36 and 37 which are connected at their upper ends to the sides of thedistributing trough 24. The lower ends of the members 36, 37, areconnected to foraminous side members 38 and 39, respectively. The lowerends of the side members 38 and 39 are connected to downwardly andinwardly sloping, foraminous bottom members 40 and 41, respectively.Thus, the grain 26 moves by gravity from the distributing trough 24through the space between the inner wall structure 28 and the outer wallstructure 35 in a mass having a thickness such that gas from within theinner wall structure 28 can be forced through the wall structures 28 and35 and the grain contained therebetween.

The module 22b is of the same construction as the module 22a describedabove and the parts have been given the same reference numerals as thosedescribed in connection with module 22a with the addition of a subscript"b". As illustrated, the upper ends of the foraminous member 36b and 37bare connected to the lower ends of foraminous members 40 and 41 ofmodule 22a.

The module 22c is of substantially the same construction as the othertwo modules 22a and 22b and accordingly, the corresponding parts will begiven the same reference numbers followed by the subscript "c" and willnot be described except as concerns certain differences in constructionwhich are hereinafter described.

Under the module 22c, the grain is collected in a trough 42 defined bytwo interconnected sloping side members 43. The grain is conducted outof the trough by means of an auger 44 which runs the length of thedrier, accordingly, the module 22c does not include the foraminousmembers 40, 41. Also, the bottom member 34c is imperforate.

Thus, as will be apparent, the grain 26 from the distributing trough 24flows around the module 22a, the module 22b, and module 22c into thetrough 42 and is conveyed out of the equipment through the auger 44.

In order to provide heat for drying the grain 26, a pair of burnerassemblies 48 are provided, one being aligned with the central portionof the module 22a and the other being aligned with the central portionof the module 22b.

Each of the burner assemblies 48 includes an inlet duct 50 which extendsfrom a source of outside air to a fan 52. The inlet duct 50 includes alouvered inlet fitting 54 which is provided with a number ofhorizontally disposed louvers 55 which are preferably angled upwardly todeflect the sound of the fan and burner upwardly and away from thoseworking in the vicinity of the drier. The inlet fitting 54 is connectedto a cylindrical duct 56 which conducts air from the louvered fitting 54to the fan 52. The fan 52 includes a driving motor 57 or the like whichis mounted in the duct 56 and a propeller type fan blade 58 which is oflarger diameter than the diameter of the duct 56. The duct 56 and thefan 52 are connected to a fan housing 60 which is of a diameter toaccommodate the fan blades 58. The fan housing 60 also includes aplurality of turning vanes 62 which are positioned to cause the aircurrents generated by the fan to move axially of the center of rotationof the fan blades 58.

In order to adjust the size of the opening between the duct 56 and thefan housing 60, a cylindrical sleeve 59 is attached to the duct 56 formovement therealong. After the proper position is determined, the sleeve59 is locked to the duct as by the bolts 61 illustrated (FIG. 3).

The fan housing 60 is connected to a cylindrical burner shroud 64 whichcontains a flame type burner 66 which is adapted to burn liquidpetroleum gas, natural gas or the like. The burner 66 illustrated is ofthe ring type, but a burner with a deflector which provides a flame witha substantial cross-sectional area also may be employed. The gas andcombustion air is conducted to the burner by a conduit (not shown) andis fed through a plurality of holes (not shown) on the side of theburner which is remote from the fan 52. The gas is ignited by ignitionmeans (not shown). The diameter of the ring burner 66 is approximatelythat of the duct 50 so that there is a circumferential space between theburner 66 and the inner walls of the duct 60.

Each of the burner assemblies 48 is mounted in an opening in the endwall 16 of the drier. As illustrated, one of the burner assemblies 48 ismounted in a position where its fan housing 60 and burner shroud 64extend into the exterior opening defined by the inner wall structure 28of module 22a. The other burner assembly 48 is mounted in a positionwhere its fan housing 60 and burner shroud 64 extend into the interiorof the opening defined by the inner wall structure 28b of module 22b.

Cooling air is supplied to module 22c by means of a fan assembly 68. Thefan assembly 68 includes a louvered inlet fitting 70 having louvers 72which are preferably angled to deflect the sound of the fan upwardly.The inlet fitting 70 is connected to an elongated, cylindrical duct 74which extends through the wall 16 of the drier and into the interioropening defined by the inner wall structure 28c of the module 22c. Thefan assembly 68 includes propeller type fan blades 76 driven by a motor78. The motor 78 and blades 76 are mounted in the duct 74.

The cooling air after it has passed through the inner wall structure28c, outer wall structure 35c and the grain contained therebetween,moves upwardly between the walls 12 and 14 and the module 22c and thelower portion of the module 22b where passage of air is blocked bylongitudinally extending plates 86. The plates 86 are horizontallydisposed and are proportioned to extend between the lower portion ofeach of the foraminous members 38b and 39b and the side walls 14 and 12,respectively. The plates 86 each extend from the end wall 16 to the endwall 18 so as to cause air from the fan assembly 68 which has passedthrough the grain to be confined in the space below the plates 86. (Theelements 80 are braces to aid in supporting wall structures 12 and 14.)

During operation, dust and organic material will build up on the plates86 and, in order to permit cleaning, the plates 86 are slidablysupported along each side in a slot defined by a pair of opposed anglemembers 88. In order to clean the upper surface of the plates 86 theyare slid outwardly through openings (not shown) in the end wall 18 ofthe drier.

In order to recycle the air from the space below the plates 86 to theburner assemblies 48, an opening 90 is provided in end wall 16 on eachside of the unit through which the air can pass. In addition, a plenum92 is provided for conducting the air from the opening 90 to the burnerassemblies 48. The plenum 92 is defined by an end wall 94 which isparallel to and spaced from the end wall 16 of the drier. The plenum endwall 94 is provided with suitable openings to support the louveredinlets 54 and 70 of the burner assemblies 48 and the fan assembly 68.Vertically extending side walls 96 and 98 interconnect the sides of theend wall 94 of the plenum 92 to the end wall 16 of the drier. The plenum92 is completed by a top wall 100 and a bottom wall 102. A clean outdoor 104 is provided in side wall 98 for removal of materials which fallto the bottom of the plenum.

In operation, grain is fed into the distributing trough 24 and fills thespace between the inner and outer wall structures of each of the modules22a, 22b and 22c. The burner assemblies 48 are ignited. Some of the airto be heated to dry the grain is drawn in from outside of plenum 92through the duct 56. Fan assembly 68 is actuated to draw cooling airinto the drier from outside of the plenum 92. The cooling air passesthrough the inner and outer wall sections 28c and 35c and through thegrain contained therebetween. In the process, the air becomes heated.Also, some heated air passes out of module 22b beneath the partition 86.The combined air streams are conducted to the plenum 92 through theopenings 90. The action of the air and gas moving outwardly from themodule 22c and the lower portion of the module 22b and then towards theopening 90 is at a low velocity and this, coupled with the changes indirection of the air stream, permits dust and organic material to settleout on members 46. In the plenum 92, the air which has entered throughopening 90 which is at a relatively high velocity decreases in velocitybecause of the large volume in the plenum and changes direction, flowinggenerally upwardly to the burner assemblies 48. The decrease in velocityand the change of direction permits an additional portion of entraineddust and organic material to fall to the bottom of the plenum 92 whereit can be periodically removed.

The upwardly moving air passes between the peripheral space between theinlet duct 56 and the fan housing 60 of each of the burner assemblies 48where it is blown by the fan blades 58, through the turning vane section62 and through the burner shroud 64 around its periphery. Thus, some ofthe air to be heated by the burner 66 is supplied from the outside, thisair being channeled centrally in the shroud 64 and directed over theburner 66 while the recycled air from the cooling section is directedthrough the shroud at its periphery to minimize contact with the flameof the burner 66.

In operation, the burner assemblies 48 are adjusted to provide heatedair and products of combustion at a temperature which is suitable forthe grain being dried. In the case of ordinary corn, the burner inmodule 22a is adjusted to provide a temperature of about 220° F. whilethe burner assembly for module 22b is adjusted to provide air at atemperature of about 190°14 200° F. When drying popcorn, rice, etc., thetemperatures are much lower in accordance with usual practices.

As particularly illustrated in FIG. 2 the heated air from module 22a andthe upper portion of module 22 above plates 85 flow upwardly out of thedrier through openings 106 controlled by adjustibly positionable doors108 in the usual manner.

Thus, the cold moist grain is first subjected to the warmest air inmodule 22a. The treatment in module 22a partially dries the grain and itmoves into module 22b where the temperature of the air is slightlyreduced to insure that the partially dried grain is not damaged by theheated air and combustion products. Thereafter, the dried, heated grainflows into module 22c and thence to auger 44 which conveys it out of thedrier. While in module 22c, ambient air is blown through the grain tocool it and this air which has been heated by the grain is conducted tothe plenum 92 where organic material and dust is dropped out and the airis subsequently introduced into the periphery of the burner shrouds.Operation has shown that this reuse of air results in a substantial fuelsavings while minimizing the danger of fire which can occur if organicmaterial and dust are passed through the burner flame.

While the danger of fire in the system which has been described isminimal, it is always present in a grain drier. Accordingly, in order tominimize damage to grain and equipment in the event of fire, emergencydump doors 110 are provided along both sides of the drier. The dumpdoors 110 are spaced apart along the length of the drier on both of itssides and are installed in the lower section of members 38c and 39c justabove metering roll assemblies 112 so that the doors 110 serve a dualpurpose as will be described.

The metering roll assemblies 112 are illustrated in FIGS. 4 and 4A andare of generally known construction. The metering roll assemblies 112are provided to control the flow of grain through the drier to obtainthe desired moisture content. If the moisture content of the dried grainis too high, the amount metered through is reduced and, if the moisturecontent is below that desired, the amount of grain metered through isincreased. The metering roll assembly 112 includes a longitudinallyextending baffle 114 which extends between the inner wall 33c and theouter wall 39c of the module 22c to provide a slot 116 which reduces thecross section of the grain path between the foraminous members. Betweenthe baffle 114 and the hopper bottom 43 there is provided alongitudinally extending shaft 118 which runs the entire length of thedrier. The shaft 118 carries a plurality of paddles or blades 120 sothat rotation of the shaft 118 and its associated paddles 120 moves thegrain from under slot 116 into the hopper 42. In order to minimizeuncontrolled flow, a longitudinally extending lip 122 is provided in thesloping side member 43 as illustrated.

Because of the action of the metering roll assembly 112, rapid movementof grain out of the drier is not possible in the event of fire or otheremergency. To accomplish such rapid dumping, the doors 110 are provided.Each of the doors 110 includes a pair of triangular end plates 124 whichare attached to a rectangular face plate 126 as illustrated. The loweredge of the face plate 126 abuts against the outer wall section 39c. Anopening 130 is provided in the wall section 39c whose ends are providedwith brackets 132. Pins 134, or the like, are passed through thetriangular end plates 124 and their associated bracket 132 so that thedoor 110 may be engaged to the wall section 39c or released and droppedoff to rapidly dump the grain merely by pulling the pins 134.

A top member 136 is provided to close the top of door 110. The topmember 136 is preferably removable and in the illustrated embodimentincludes upstanding flanges 138a, b, c, and d, flanges 138a and 138bbeing detachably connected to the end plates 124 as by bolts 140. Thus,in addition to providing a means to dump the grain rapidly from thedrier, the top member 136 may be removed with the door 110 in theposition shown in FIGS. 4 and 4A to provide access to the metering rollassembly 112. It is thus possible to remove tramp materials which maybecome lodged in the slot 112 or under the paddles 120 without emptyingthe grain from the drier.

During operation, dust and organic material tend to accumulate on theplates 34, 34b and 34c and on the inner walls of modules 22a, 22b and22c. In order to rapidly clean those areas, the end wall 18 is providedwith a large opening 141 which is covered with a power operated doorassembly 142 which will open and close the opening 141. In the openposition, the fans 58 and 76 are operable to rapidly blow foreignmaterial which is in each of the modules out of the opening 141 withouta substantial interruption in the operation of the drier.

The door assembly 142 is particularly illustrated in FIG. 5. Theassembly 142 includes a plate 143 which is proportioned to be larger ineach dimension than the opening 141 in the wall 18 as shown by thedotted outline in FIG. 5. The lower edge of plate 141 is hingidlyattached to the wall 18 by the hinge members 145 so that it can folddown against its associated bottom member 34. The plate 143 is providedwith a pair of spaced apart brackets 144, and to each of the brackets144 there is hingedly attached one end of a link 146. The other end ofeach of links 146 is hingedly attached to a crank arm 148 rigidlyattached to a shaft 150. The shaft 150 is journalled in brackets 152which are supported on the end wall 18, the axes of the hingedconnections at the ends of links 144 being parallel to the axis of theshaft 150 so that the rotation of the shaft 150 causes the plate 143 tomove inwardly relative to the opening 141.

Rotation of the shaft 150 is preferably effected by a pneumaticallyoperated cylinder 153 attached to the wall 18 by brackets 155. This isaccomplished by connecting the piston rod 156 of the cylinder 153 to acrank arm 157 rigidly attached to the shaft 150. Pressurized air isconducted to the cylinder 153 through conduit 158. Thus, pressurizationof the cylinder 153 extends the piston rod 156 and rotates the shaft150. This causes the plate 143 to swing inwardly against the airpressure within the drier, thus, permitting the fans to blow outaccumulated dust and organic material.

As illustrated, an accumulator 160 is mounted on the brackets 155adjacent the cylinder 153. The accumulator includes a chamber which isconnected by a conduit 162 to the pneumatic cylinder 153 to receive theair which is displaced by the piston when the door is opened. Thedisplaced air will be at an elevated pressure and, when operatingpressure is released from the cylinder 153, the pressure in theaccumulator 160 together with the air pressure from the fan on the plate143 will cause the plate to rotate about the hinge 145 to the closedposition. The closing force may be increased by reducing the volume inthe accumulator 160 as by partially filling it with oil or the like.

In FIGS. 6 and 7 there is illustrated a portable drier which embodiesvarious of the features of the invention. The grain to be dried isconfined between inner foraminous wall sections 170 and outer foraminouswall sections 172. The grain path, in cross-section (FIG. 7) includestwo spaced apart, vertically extending runs 174 and 174a which merge attheir upper ends at the distributing trough 177. The lower end of eachof the grain paths 174 and 174a is provided with an auger 176 and 176ato effect removal of the dried grain. As in the case of the drier whichhas previously been described, the upper portion of the grain paths 178are heated and the lower portion of the grain paths 180 is cooled. Theseareas are separated by an imperforate partition 182 which extendsbetween the foraminous inner wall sections 170. The bottom of thecooling section 180 is defined by the horizontally extending partition184.

Heating of the grain is effected by a burner assembly 48' which isidentical to the burner assemblies 48 which have been described, theburner shroud 64' extending into the space defined by the upper portionsof the inner foraminous sections 170 and the partition 182.

Cooling air is drawn through the grain in the area between thepartitions 182 and 184 by a fan 186 mounted in the end wall 188 of thedrier. In order that the heated moist air from the heated section is notdrawn through the cooling section, weather shields 190 are attached tothe outer side of the foraminous members 172 in the heated section ofthe grain paths l78 to direct the heated air upwardly as shown by thearrows 192.

A weather shield 194 is also provided for the cooling section of thegrain paths 180 which includes a control damper 196 for adjusting theamount of air admitted to the cooling section 180.

A plenum 198 is provided for the burner assembly 48' and the fan 186,the plenum being attached to the end wall 188 of the drier. As shown inFIG. 6 the plenum 198 includes an end wall 200 which receives thelouvered inlet 54' for the burner assembly 48', a top 202, side members204 and a bottom 206. The end wall 200 of the plenum is provided with acleanout door 208 (normally closed during operation) for removingaccumulated dirt and organic matter as required.

In order to aid in settling out materials entrained in the cooling airafter it has passed through the grain mass, a pair of spaced-apartpartitions 210 are disposed in the cooling section. The partitions 210run the length of the drier and are spaced inwardly of the foraminouswall sections 170. The partions 210 are vertically extending and aresupported on the bottom partitions 184.

In operation, the cooling air is drawn through the confined grain by thefan 186 and is caused to move upwardly by the partitions 210 so that thechange of direction and the low velocity causes some entrained materialsto settle out. The air then passes between the top of partition 210 andbottom partition 182 to fan 186. The air from the fan 186 is dischargedinto the plenum 198 where the cross-sectional area of the flow path isincreased thus decreasing its velocity. Also, its direction is changed,both of which actions cause additional materials to settle out. The airis then drawn between the duct 56' and the housing or shroud 64' whereit flows downstream around the periphery of the burner 66, thus,minimizing contact of this air with the direct flame from the burner.Again, the outside air which is drawn through the inlet 54' is channeledthrough the central area of the shroud 64' part of the burner 66'.

The heated air is forced through the grain mass to effect its drying andthen is discharged upwardly by the action of the weather shields.

FIG. 8 shows another mode of operation for the drier illustrated inFIGS. 6 and 7. In this mode, a portion of the heated air is recycledinto the cooling section and the grain is cooled at a location remotefrom the drier. Such operation increases the drying capability of thedrier without greatly increasing fuel consumption.

In this mode, the dampers 196 are closed and a horizontally disposed,longitudinally extending partition 212 is provided on each side of thedrier between the weather shields 190 and the outer foraminous wallsections 172. The partition 212 is located above the partition 182 sothat a substantial portion of the heated gases from the burner 48' areconducted through the cooling section. Entrained materials are settledout in the manner which has been described. In this mode, the cleanoutdoor 208 is opened and its position adjusted to balance the air in theplenum and to maintain the moisture level in the recirculated gases at asatisfactory level.

Various of the features of the invention which are believed to be neware set forth in the appended claims.

What is claimed is:
 1. An improvement in a grain dryer having apassageway defined by imperforate walls and foraminous walls and a fandisposed for moving air from outside said passageway into saidpassageway and into said foraminous walls, comprising:an opening formedin said passageway and being disposed remotely from said fan forselectively allowing air and foreign material to be blown out of thepassageway through said opening; a plate mounted inside the passagewayfor selectively covering said opening; means for supporting said plateadjacent said opening; and actuation means attached to said plate foreffecting movement of said plate between a closed position immediatelyadjacent to and covering said opening and an open position disposedinwardly from said opening inside the passageway to selectively coverand uncover said opening whereby air movement produced by said fan blowsforeign material off of said walls and out of said opening.
 2. Theimprovement of claim 1 wherein said means for supporting comprises ahinge positioned to hingedly support said plate for movement into thepassageway.
 3. The improvement of claim 2 wherein said actuation meansis operable to effect movement of said plate into said passageway touncover said opening and to hold said plate in the open position withinsaid passageway so that the air blowing through said opening tends tourge said plate toward said opening when said plate is in the openposition.
 4. The improvement of claim 2 wherein said actuation means isoperable to effect pivotal movement of said plate about said hingethrough an angle of less than 90° to an open position whereby air movedby said fan through said opening tends to urge said plate toward saidopening.
 5. The improvement of claim 1 wherein said plate is larger thansaid opening and is disposed over an covering said opening so that airpressure within said passageway created by said fan holds said plate ina closed position covering said opening.
 6. The drier of claim 1 whereinsaid actuation means for effecting movement of said plate furthercomprises a pneumatic cylinder, said pneumatic cylinder being connectedto an accumulator whereby the application of actuating air pressure tosaid pneumatic cylinder effects movement of said plate and air in saidcylinder flows under pressure into said accumulator whereby release ofactuating pressure on said cylinder permits the pressure in saidaccumulator and the pressure caused by air currents generated by saidfan to cause said plate to move into sealing engagement with said endwall.